[opus] running at 44.1K but with standard frame sizes

[Marc Lindahl]

Hi Tim,
Thanks for the detailed breakdown!
Now clearly understand the tradeoff involved in specific terms.  
Having a list of which options are disabled/enabled for custom mode would be a great addition to the documentation.

Combined with the previous comments I'm more than convinced that for my immediate needs, I should focus on the standard coder. 

Thanks again.

On Jun 15, 2013, at 2:18 PMEDT, Timothy B. Terriberry wrote:

> Marc Lindahl wrote:
>> Of course, I'm setting up a bunch of tests to evaluate these, what I was asking was more along the lines of,
>> If you set up the same exact, including the sample rate, do you get the same results (e.g. same code path, calculations, etc.?)
> 
> If you configure a custom mode with the standard parameters (48 kHz 
> sampling rate and a frame size of 120, 240, 480, or 960), the encoded 
> format is _exactly_ equivalent to a standard Opus mode, and can even be 
> decoded by a non-custom Opus decoder.
> 
> However, there is a bunch of analysis that runs in opus_encoder.c that 
> is not enabled for custom modes. A fixed-point standard Opus encoder 
> with OPUS_APPLICATION_RESTRICTED_LOWDELAY, OPUS_BANDWIDTH_FULLBAND, and 
> OPUS_SET_FORCE_CHANNELS should give identical results.
> 
> In floating point, you will need to call the non-public run_analysis() 
> API and use the CELT_SET_ANALYSIS() encoder ctl to get equivalent results.
> 
> Using OPUS_APPLICATION_RESTRICTED_LOWDELAY disables SILK and automatic 
> voice/music detection.
> 
> Forcing OPUS_BANDWIDTH_FULLBAND in the standard modes disables automatic 
> bandwidth detection... you could hook something equivalent up for Opus 
> Custom, but CELT_SET_END_BAND_REQUEST is not exposed in the public API 
> (and you are _required_ to use end band numbers compatible with standard 
> Opus modes (13, 17, 19, or 21), or the encoder will fail).
> 
> OPUS_SET_FORCE_CHANNELS() will disable automatic rate-dependent 
> switching between mono and stereo. You can hook up something equivalent 
> by aping the code in opus_encoder.c.
> 
> There may be other differences I've forgotten. In general, custom modes 
> are not well-tested (in comparison to the standard modes).
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